Re: subpage reads/writes with fsl_elbc_nand driver

[Boris Brezillon <bbrezillon@xxxxxxxxxx>]

On Thu, 31 Jan 2019 14:24:15 +0000
Rasmus Villemoes <rasmus.villemoes@xxxxxxxxx> wrote:

> I'm in the process of upgrading a board from an old 3.14-based kernel
> with quite a few out-of-tree patches to one based on 4.19, hopefully
> with much fewer such patches.
> 
> In order to even get the new kernel to mount the existing root
> filesystem, I've had to apply the hacks below:
> 
> --- a/drivers/mtd/nand/raw/nand_base.c
> +++ b/drivers/mtd/nand/raw/nand_base.c
> @@ -6657,6 +6657,11 @@ static int nand_scan_tail(struct mtd_info *mtd)
>                 pr_warn("WARNING: %s: the ECC used on your system is too
> weak compared to the one required by the NAND chip\n",
>                         mtd->name);
> 
> +       if (IS_ENABLED(CONFIG_ML300PCM31)) {
> +               pr_warn("setting NAND_NO_SUBPAGE_WRITE bit\n");
> +               chip->ecc.write_subpage = NULL;
> +               chip->options |= NAND_NO_SUBPAGE_WRITE;
> +       }
>         /* Allow subpage writes up to ecc.steps. Not possible for MLC
> flash */
>         if (!(chip->options & NAND_NO_SUBPAGE_WRITE) && nand_is_slc(chip)) {
>                 switch (ecc->steps) {
> @@ -6681,8 +6686,12 @@ static int nand_scan_tail(struct mtd_info *mtd)
>         /* Large page NAND with SOFT_ECC should support subpage reads */
>         switch (ecc->mode) {
>         case NAND_ECC_SOFT:
> -               if (chip->page_shift > 9)
> -                       chip->options |= NAND_SUBPAGE_READ;
> +               if (chip->page_shift > 9) {
> +                       if (IS_ENABLED(CONFIG_ML300PCM31))
> +                               pr_warn("setting of NAND_SUBPAGE_READ
> bit has been patched out\n");
> +                       else
> +                               chip->options |= NAND_SUBPAGE_READ;
> +               }
>                 break;
> 
> Without the latter, I get
> 
>     [    0.833134] fsl,elbc-fcm-nand fff00000.nand: fsl_elbc_cmdfunc:
> error, unsupported command 0x5.
>     [    0.841822] fsl,elbc-fcm-nand fff00000.nand: read_buf beyond end
> of buffer (14 requested, 0 available)
> 
> and then an endless loop of errors. With that hunk, I get a little
> longer, but without the former the boot stops at
> 
>     [    0.918927] ubi0 error: validate_ec_hdr: bad VID header offset
> 2048, expected 512
>     [    0.926549] ubi0 error: validate_ec_hdr: bad EC header
>     [    0.931745] Erase counter header dump:
>     [    0.935547]        magic          0x55424923
>     [    0.939344]        version        1
>     [    0.942359]        ec             9
>     [    0.945373]        vid_hdr_offset 2048
>     [    0.948610]        data_offset    4096
>     [    0.951879]        image_seq      1882958541
>     [    0.955678]        hdr_crc        0x1a47f3d3
>     ...
>     [    1.059976] ubi0 error: ubi_io_read_ec_hdr: validation failed for
> PEB 0
>     [    1.066669] ubi0 error: ubi_attach_mtd_dev: failed to attach
> mtd0, error -22
>     [    1.073824] UBI error: cannot attach mtd0
>     [    1.083983] VFS: Cannot open root device "ubi0:rootfs" or
> unknown-block(0,0): error -19
> 
> I have
> 
>        nand-ecc-mode = "soft";
>        nand-ecc-algo = "bch";
>        nand-ecc-strength = <4>;
>        nand-ecc-step-size = <512>;
> 
> in .dts. Is there some device-tree setting/quirk I can use to avoid the
> above hacks? Alternatively, can someone provide some hints on how a
> mainlinable patch achieving the above would look?

Just pass ubi.mtd=<part-name>,<page-size> on the command line. This way
the VID header will be read/written from/to the second page instead of
the 2nd subpage of the first page.

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